There are two types of rivers in the country viz: perennial and non-perennial rivers. Perennial are those rivers in which water remains available throughout the year and non-perennial are rain-fed rivers, in which water flows only during the monsoon. Rivers in the country are polluted mainly due to discharge of untreated and partially treated sewage from cities/towns and industrial effluents in their respective catchments, problems in operation and maintenance of sewage/effluent treatment plants, lack of dilution and other non point sources of pollution. Rapid urbanization and industrialization have compounded the problem.
Cleaning/rejuvenation of rivers is an ongoing activity. It is the responsibility of the States/UTs and local bodies to ensure required treatment of sewage and industrial effluents to the prescribed norms before discharging into river and other water bodies, coastal waters or land to prevent and control of pollution therein. For conservation of rivers, this Ministry has been supplementing efforts of the States/UTs by providing financial and technical assistance for abatement of pollution in identified stretches of rivers in the country through the Central Sector Scheme of Namami Gange for rivers in Ganga basin, and Centrally Sponsored Scheme of National River Conservation Plan  for other rivers. Further, priority for effective rejuvenation of small rivers has been accorded under the Mahatma Gandhi National Rural Employment Guarantee Scheme .
Proposals for pollution abatement works in the towns along polluted river stretches are received from the States/UTs from time to time for consideration under NRCP and sanctioned based on their prioritization, conformity with NRCP guidelines, availability of plan funds, etc.
NRCP has so far covered polluted stretches on 34 rivers in 77 towns spread over 16 States in the country with the project sanctioned cost of Rs.5965.90 crore, and inter-alia, a sewage treatment capacity of 2522.03 MLD has been created. Under Namami Gange programme, a total of 346 projects including 158 projects for sewage treatment of 4948 MLD and sewer network of 5213 km, have been sanctioned at a cost of Rs.30235 crore.
In addition, sewerage infrastructure is created under programs like Atal Mission for Rejuvenation & Urban Transformation  and Smart Cities Mission of Ministry of Housing & Urban Affairs.
As per the Provisions of Environment  Act, 1986 and Water , Act 1974, industrial units are required to install effluent treatment plants  and treat their effluents to comply with stipulated environmental standards before discharging into river and water bodies. Accordingly, Central Pollution Control Board , State Pollution Control Boards  and Pollution Control Committees  monitor industries with respect to effluent discharge standards and take action for non-compliance under provisions of these Acts.
Besides, in compliance of the orders of National Green Tribunal  in Original Application No.673/2018 regarding rejuvenation of polluted river stretches in the country, States/UTs are required to implement approved action plans for restoration of the polluted stretches in their jurisdiction as identified by CPCB and published in their report of 2018, within the stipulated timelines. As per the orders of NGT, regular review on implementation of action plans is undertaken in the States/UTs and also at Central level.
This information was given by the Minister of State for Jal Shakti & Food Processing Industries, Shri Prahlad Singh Patel in a written reply in the Lok Sabha today.